1. Field of the Invention
The invention is based on an optical sensor for rotational movements of the generic type having a laser beam source, a device for splitting the beam emitted by the laser beam source into first and second partial beams, an annular optical fiber arrangement into which the first partial beam is coupled in a first direction and the second partial beam is coupled in a second direction, with the first and second directions being opposite, and a photodetector into which first and second partial beams are coupled out of the annular optical fiber arrangement are supplied. An optical sensor of this type is known from the publication by K. HOTATE and S SAMUKAWA, "Drift reduction in an optical heterodyne fiber gyro," Applied Optics, Vol. 29, No. 9, Mar. 20, 1990, pp. 1345-1349. The Sagnac effect, which occurs in a fiber optical gyro, is the basis of the known sensor. The beam generated by a laser diode is split into two partial beams with a grating and a beam splitter, and subsequently coupled into an optical fiber disposed in annular form. One partial beam passes through the fiber clockwise, and the other partial beam passes through counterclockwise. The beams coupled out of the fiber are conducted through the beam splitter and impact upon an acousto-optical modulator that superposes the beams. The grating and the acousto-optical modulator, whose angles of diffraction are identical, are disposed symmetrically with respect to the beam splitter. A photodetector receives a non-refracted portion of the beam that has circulated clockwise in the fiber, the frequency of the beam being identical to the frequency of the semiconductor laser beam. Moreover, the photodetector receives a diffracted portion of the beam rotating counterclockwise in the fiber and having a frequency that is altered by the magnitude of the frequency generated by the acousto-optical modulator, with respect to the beam produced by the semiconductor laser. The photodetector emits as an output signal the altered frequency designated as the heterodyne frequency. A rotation of the optical fiber results in a phase shift between the signal emitted by the photodetector and the signal that controls the acousto-optical modulator.
The authors of the publication concede that this above-described optical sensor for rotational movements has drawbacks with regard to zero-point stability that are particularly a function of a temperature drift of the acousto-optical modulator. Thus, in one feature of the known device, a reference path is incorporated that represents an optical short-circuit with respect to the annularly-disposed optical fiber, and upon which the measuring effect has no effect. The measurement process is subdivided into two time segments. The phase of the output signal of the photodetector is stored during the first segment, which must be shorter than the running period of the optical beam through the annularly-disposed acousto-optical modulator, and the two partial beams pass through the optical short-circuit path practically without a time delay. During the second segment, the partial beams coupled out of the annular optical fiber, which at this point have already passed through this fiber, are received by the photodetector. The measurement result is determined through comparison of the phase position of the photodetector signal obtained in the second segment with the photodetector signal obtained in the first segment.
The object of the invention is to provide an optical sensor for rotational movements that can be realized with simple means.